1. Field of the Invention
The present invention generally relates to a method and an apparatus for time-sequentially displaying acquired data as a trend graph on a display unit such as CRT (cathode-ray tube). More specifically, the present invention is directed to such a method and apparatus capable of displaying a trend graph by a middle enlarged display portion, and upper and lower reduced display portions on the display screen.
2. Description of the Related Art
In a trend graph display system, acquired data is normally displayed in reduced form in order to save a display area. As a consequence, when it is desired that detailed data be displayed, a portion of the original trend graph must be enlarged and displayed on the monitor screen.
FIG. 1 represents a typical display condition of the conventional trend graph displaying method where an overall original trend graph has been enlarged. Since only a portion of acquired data is displayed on the display screen 1 which cannot entirely display the enlarged overall trend graph, a hatched portion of a display position indication 6 is actually displayed as the trend graph thereon. Therefore, to display other desirable data of the enlarged trend graph, a pair of scroll keys 5A and 5B are manipulated so that the actual display positions of the enlarged trend graph are sequentially changed.
As apparent from the conventional trend graph representation shown in FIG. 1, since only a part of acquired data is displayed when the overall trend graph is enlarged, or expanded, it is impossible to compare this displayed data portion (i.e., a portion of the enlarged trend graph) with other undisplayed data portion of the overall acquired data. Moreover, the scroll keys 5A and 5B must be manipulated in order to display the desirable data on the screen 1. In this case, a definite decision may not always be made which scroll key 5A or 5B must be operated. This is because it may be difficult to judge which direction, the displayed trend graph must be scrolled. These drawbacks are mainly caused by the fact that the overall trend data cannot be displayed on the screen when the overall original trend graph is enlarged.
The present invention has been made in an attempt to solve the above-described drawbacks of the conventional trend graph displaying method, and therefore has an object to provide a novel method for displaying overall trend data even when the original trend graph is partially enlarged. Another object of the present invention is to provide an apparatus capable of displaying overall trend graphic data under the condition that the original trend graph is partially enlarged.